The Effect of Cr on Ageing Of Co Containing Cu-Bearing 0.2 wt% C Steel

Date

2023-12-11

Author

Koluaçık, Ekin

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Despite harmful effects on steel as a trace element, Cu is preferably added to steel alloys for age hardening. This thesis study aims to investigate the effect of Cr on Co-containing Cu-bearing 0.2 wt% C steels with martensitic and bainitic microstructures. To investigate this effect, two alloys were studied. One of the alloys, namely A1 does not contain Cr but A2 have 0.6 wt% Cr. Furthermore, the reason of Cr addition is also to improve the hardenability. Moreover, Co is known for the promotion and acceleration of bainitic transformation. After casting and subsequent homogenization, quenching and isothermal treatments are applied to different specimens to obtain martensitic and/or bainitic microstructures. The specimens are aged at 450 °C and 500 °C for 100 minutes, 200 minutes or 300 minutes. The microstructures are investigated under optical microscope and SEM. The hardness measurements are carried out. After quenching, alloy A1 exhibits Widmanstätten ferrite and granular bainite besides martensite in its microstructure due to low hardenability. In contrast to martensitic A2 specimen, the specimens of both A1 and A2 which contain either Widmanstätten ferrite or bainitic ferrite respond to ageing treatment at 450 °C. It is concluded that the bainitic and Widmanstätten ferritic structures enhance the Cu precipitation in contrast to martensitic structure.

Subject Keywords

bainite, martensite, copper, cobalt, chromium

URI

https://hdl.handle.net/11511/107784

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Graduate School of Natural and Applied Sciences, Thesis